In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipment units (UE) such as mobile telephones (“cellular” telephones) and laptops with wireless capability, e.g., mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks is also called “NodeB”, “B node”, or (in LTE) eNodeB. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions of radio access networks, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). An entity known as the Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
Specifications for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) are ongoing within the 3rd Generation Partnership Project (3GPP). Another name used for E-UTRAN is the Long Term Evolution (LTE) Radio Access Network (RAN). Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected directly to a core network rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller (RNC) node are performed by the radio base stations nodes. As such, the radio access network (RAN) of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller (RNC) nodes. The evolved UTRAN (E-UTRAN) comprises evolved base station nodes, e.g., evolved NodeBs or eNBs, providing evolved UTRA user-plane and control-plane protocol terminations toward the wireless terminal.
In LTE as in other radio access technologies, it is advantageous for the network to know with reasonable accuracy the geographical position of a wireless terminal (UE). In fact, some countries or jurisdictions mandate that the network be able to locate the UE within a prescribed distance range (e.g., a few tens of meters) and within a stipulated time duration. This requirement is often imposed for facilitating services to UE, such as emergency services to a person operating the UE, or for security management reasons.
Knowledge of the UE's geographical whereabouts typically comes from the UE determining its own geographical position and reporting that geographical position to the network, as well as to the person operating the UE. This capability for the person operating the UE to know his/her location can be of considerable value to the UE operator, and indeed subscriptions to such location-reporting service can be a source of revenue for a network operator.
The Global Navigation Satellite System (GNSS) is the standard generic term for satellite navigation systems that enable subscribers such as UE operators to locate their position and to acquire other relevant navigational information. The global positioning system (GPS) and the European Galileo positioning system are well known examples of GNSS.
Not only Global Navigation Satellite System (GNSS) but also non-GNSS positioning methods have been employed for determining UE position. According to one proposal, in some contexts a GNSS based-positioning method may be employed as a primary positioning technique, while a non-GNSS positioning method may be employed as a secondary or backup positioning technique. See, in this regard, RP-080995, Work Item, “Positioning Support for LTE”, Qualcomm (Rapporteur), which is incorporated herein by reference. Other UE positioning techniques are described, e.g., in the following: (1) RP-070926, Study Item, “Evaluation of the inclusion of Pattern Matching Technology in the UTRAN”, Polaris Wireless (Rapporteur); and (2) RP-090354, Work Item, “Networ12-Based Positioning Support for LTE”, True Position (Rapporteur), both of which are incorporated herein by reference in their entirety.
The non-GNSS positioning methods are often also referred to as terrestrial positioning methods. These terrestrial positioning methods usually determine UE position on the basis of signals measured by the UE and/or radio network nodes such as base station. Examples of such signals and methods include cell identity based methods; network-based methods which detect the uplink time difference of arrival (U-TDOA) of signals at different base stations; UE-based methods which observe the time difference of arrival (OTDOA) of signals from three or more cells; and fingerprinting or pattern matching positioning methods.
Some of these terrestrial positioning methods such as cell ID based and pattern matching positioning technology make use of normal UE neighbor cell measurements such as the detected cell identity, received signal strength, path loss etc. On the other hand, certain methods such as U-TDOA and OTDOA require specific measurements. Some of the measurements such as time difference of arrival can also be reused for other purposes such as time alignment at handover, support for cell synchronization, etc.
In the 3rd Generation Partnership Project (3GPP), a layer 3 protocol known as the Radio Resource Control (RRC) layer defines various RRC states to describe the usage of radio resources for the UE. There is a difference in the number of states in UTRAN on the one hand, and LTE on the other hand.
The 3rd Generation Partnership Project (3GPP) also supports a feature known as discontinuous reception (DRX). Discontinuous reception (DRX) enables a UE to save power by turning off some or all of its radio circuitry when not needed, thereby increasing battery lifetime of the UE. Discontinuous reception (DRX) is described and utilized in another perspective in U.S. patent application Ser. No. 12/475,953, filed Jun. 1, 2009, entitled “USING MOBILITY STATISTICS TO ENHANCE TELECOMMUNICATIONS HANDOVER”, which is incorporated herein by reference in its entirety.
In UTRAN there are several RRC states: Idle state; CELL_PCH state; URA_PCH state; CELL_FACH state; and CELL_DCH state. In E-UTRAN in idle state the UE is known on a tracking area level, which comprises of multiple set of cells (e.g. 100-300 cells). Similarly in the CELL_DCH state the UE uses dedicated radio resources that are not shared with other UEs; the UE is known on a cell level according to its current active set; and, the UE can use dedicated transport channels, downlink and uplink shared transport channels, or a combination of transport channels. In the UTRAN CELL_FACH state no dedicated physical channel is assigned to the UE; the UE continuously monitors a FACH channel in the downlink; and, the UE is assigned a default common or shared transport channel in the uplink (e.g., RACH). In the UTRAN CELL_PCH or URA_PCH state no dedicated physical channels is assigned to the UE; no uplink activity is possible; and, the UE receives paging or broadcasting information from the UTRAN. Discontinuous reception (DRX) is now used in all these UTRAN RCC states according to 3GPP release 7 and beyond. But for the CELL_FACH and CEL_DCH states the allowed DRX cycles are much shorter. Specifically, for CELL_DCH max DRX cycle=40 ms.
For LTE there are only two RRC states: Idle state and Connected state. DRX is used in both LTE states, with the DRX cycles in both states ranging from 10 ms to 2.56 sec.
Although the ensuing discussion and description focus on discontinuous reception (DRX) operation in LTE, it should be understand that the discussion and descriptions are not limited to LTE but can apply to other environments including UTRAN.
A DRX “cycle” comprises an “on duration” and a “DRX period”. During the “on duration” portion of the cycle the user equipment unit (UE) should monitor a channel known as the Dedicated Physical Control CHannel (PDCCH) for scheduling assignments in RRC connected state. In LTE the paging is also mapped on PDCCH. Therefore UE in idle state also monitors PDCCH for the reception of paging. During the “DRX period” the UE can skip reception of downlink channels for battery saving purposes. Thus DRX has a tradeoff between battery saving and latency: on the one hand, a long DRX period is beneficial for lengthening the battery life of the UE; on the other hand, a shorter DRX period is better for faster response when data transfer is resumed.
In general the DRX function is configured and controlled by the network. The UE behavior is based on a set of rules that define when the UE must monitor the Dedicated Physical Control CHannel (PDCCH) for scheduling assignments.
When the UE does not have an established radio-resource control (RRC) connection, i.e., when no radio bearers are configured for radio transmission involving the UE, the UE is generally “asleep” abut wakes up and monitors the paging every DRX cycle.
On the other hand, when the UE has an RRC connection and the DRX function is operative (e.g., RRC connected state in LTE), the DRX function is characterized by the aforementioned DRX cycle, the aforementioned on-duration period, and an inactivity timer. The UE wakes up and monitors the PDCCH at the beginning of every DRX cycle for the entire on duration period. When a scheduling message is received during an “on duration”, the UE starts the inactivity timer and monitors the PDCCH in every subframe while the inactivity timer is running. During this period, the UE can be regarded as being in a reception mode. Whenever a scheduling message is received while the inactivity timer is running, the UE restarts the inactivity timer. When the inactivity timer expires the UE moves back into another DRX cycle. If no scheduling assignment is received, the UE falls asleep again.
Thus, in E-UTRAN or LTE the DRX feature is used in both idle and RRC connected modes. The aforementioned positioning measurements are typically done in connected mode. Furthermore in E-UTRAN, there can be a wide range of DRX cycles (e.g., cycle lengths) for use in the RRC connected mode as allowed by the network. For example, the DRX (i.e., the time length of the DRX cycle) can vary between 10 ms to 2.56 seconds. With the increase in the DRX cycle, there is more time between measurements, and thus the measurement performance of measurement quantities can deteriorate since the UE may only sparsely (e.g., less frequently) measure on signals received from the cells. When the UE is in the DRX state the measurement period can also be set to be longer and the length of the measurement period can vary with the DRX cycle.
Measurement period is a concept well known in telecommunications, e.g. UTRAN and E-UTRAN. As illustrated in FIG. 16, one measurement period requires comprises several samples (e.g. 4-5 samples) from each of the cells being samples. The number of samples can vary, e.g., can be implementation-specific. FIG. 16 illustrates a situation in which there are (by way of example) four cells whose signals are measured, and four samplings of each cell. In a non-DRX mode the measurement period is standardized to be 200 milliseconds. The samplings for the cells can be averaged over the measurement period.
Typically the measurement period of a measurement quantity is K times the DRX cycle, e.g. 5 times the DRX. As an example for DRX cycle of 2.56 seconds the measurement period of reference signal received power (RSRP), which is LTE measurement quantity, is approximately 10.28 seconds. During a single measurement period the wireless terminal (UE) is also capable of performing a particular type of measurement (such as RSRP) from certain number of cells, e.g. 6 or 8 cells including the serving cell. The measurement periods of all standardized measurement quantities for the continuous reception (non DRX case) and for all allowed DRX cycles are pre-defined in the 3GPP standard. Similarly the number of cells from which the UE is required to perform certain measurement quantity over the measurement period is also specified in the standard.
So if the measurement period of the positioning measurement is also extended due to DRX, then the measurement reporting delay will increase, and thus the response time in determining the wireless terminal (UE) positioning will be longer. These phenomena can negatively impact accuracy of a determination of wireless terminal (UE) position.
The accuracy of UE positioning determination can not only be affected by discontinuous reception (DRX), but by discontinuous transmission (DTX) as well. That is, discontinuous transmission (DTX) such as discontinuous power control and use of idle gaps for measurements, can also affect the positioning performance. Discontinuous transmission (DTX) is characterized by periodic pattern of activity or transmission followed by relatively longer inactivity or idle periods.
In case of uplink discontinuous transmission (DTX) the base station will less frequently (e.g., sparsely) receive signals from the UE, and hence would have less opportunity for performing measurements. A longer discontinuous transmission (DTX) will lead to longer measurement period and thus longer response time in determining the UE position. For instance, a round trip time (RTT) measurement done at the base station for network based positioning will be delayed when discontinuous transmission (DTX) is used.
In UTRAN, discontinuous transmission (DTX) is characterized by discontinuous power control channel (DPCCH) and is used to reduce the interference and UE power. Similarly other idle gaps such as compressed mode gaps and measurement gaps are used in UTRAN and E-UTRAN respectively.
Positioning measurements are typically performed in RRC connected state. In legacy systems such as UTRAN FDD and TDD, some positioning specific measurements and corresponding procedures exist. In these legacy systems the longest allowed discontinuous reception (DRX) cycle in RRC connected state is limited to 40 ms, and the measurement period of all UE measurements (including positioning measurements) scales with the DRX cycle. For instance, the WCDMA SFN-SFN type 2 positioning related measurement is performed, when UE receiver is active, simultaneously to data reception. This means, depending upon the DRX cycle, the measurement period in DRX is longer than in the non DRX case. However due to shorter DRX (40 ms) in UTRAN CELL_DCH, the impact of the DRX on the positioning performance is not very significant.
In E-UTRAN the DRX cycle in RRC connected state can range up to 2.56 seconds. In DRX state traditionally the measurement period of a measurement quantity is K times DRX cycle, e.g. 10.28 seconds for 2.56 seconds DRX cycle assuming scaling factor of 5. This level of measurement period is very long for the positioning measurement. Therefore scaling of the measurement period when discontinuous reception (DRX) in E-UTRAN is used is not desirable. This is because the extended measurement period will adversely affect the positioning accuracy (i.e. response from UE) and might prevent achieving the positioning accuracy requirements.
The discontinuous transmission (DTX) may also impact the accuracy and response time of positioning performance. Especially uplink measurements such as round trip time (RTT) can be delayed if the UE is operating under longer DTX level or cycle.